Reciprocating piston pump surface treatment process

ABSTRACT

A process for treating rods and cylinders for use in reciprocating piston pumps is provided which yields a substantial increase in wear over the chrome coatings of the prior art. A base material of stainless steel 17-4ph is heat treated in the range generally from H-900 to H-1150. Once the material is pretempered, an ion nitriding process is applied. With this process, the hardness can be increased from the standard 17-4 hardness of RC-44 max to a desired hardness of RC-65 to 75.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. Applicationserial No. 60/257,419, filed Dec. 22, 2000.

BACKGROUND OF THE INVENTION

[0002] Reciprocating piston pumps (primarily double-acting but alsosingle-acting) have been used for pumping paints and similarly viscousabrasive materials for many years. To date, the most successfultraditional finishing of the cylinders and rods in such products are tochrome-finish surfaces of those parts.

SUMMARY OF THE INVENTION

[0003] It is an object of this invention to provide rods and cylindersfor use in reciprocating piston pumps which provide a substantialincrease in wear over the chrome coatings of the prior art.

[0004] Towards this end, for a base material, a stainless steel of agrade known as 174ph. The base material is then heat treated in therange generally from H-900 to H-150. Non-standard heat treatment tempssuch as H-950 can also be used. Once the material is pretempered, theion nitriding process is then applied. With this process, the hardnesscan be increased from the standard 17-4 hardness of RC-44 max to adesired hardness of RC-65 to 75. These hardnesses can be controlled towithin 0.001 of the thickness effective case depth and go as deep as0.010 on the 17-4 material. These hardnesses are the equivalent orhigher than the best chrome coatings available.

[0005] These and other objects and advantages of the invention willappear more fully from the following description made in conjunctionwith the accompanying drawings wherein like reference characters referto the same or similar parts throughout the several views.

A BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is an exploded view of a pump capable of using the instantinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0007] Towards this end, for a base material for rod 201 and cylinder206, a stainless steel of a grade known as 17-4ph is used. The basematerial is then heat treated in the range generally from H-900 toH-1150. Non-standard heat treatment temps such as H-950 can also beused. Once the material is pretempered, the ion nitriding process isthen applied. With this process, the hardness can be increased from thestandard 17-4 hardness of RC-44 max to a desired hardness of RC-65 to75. These hardnesses can be controlled to within 0.001 of the thicknesseffective case depth and go as deep as 0.010 on the 17-4 material. Thesehardnesses are the equivalent or higher than the best chrome coatingsavailable.

[0008] The ion nitriding process (which is generally well known) is nota coating and will not flake off or have poor adhesion to the basematerial. Using an ion nitriding process also eliminates one grindingoperation and the wear surface of the part is whatever the 17-4 materialhas been prefinished to. Accordingly, the surface does not have smallmicrocracks covering the entire surface, as was the case with prior artcoatings and finishes. This eliminates potential premature failures dueto erosion through the surface cracks. Most importantly, use of thisprocess provides an increase in pump life of up to four times over thestandard part finishes such as chrome.

[0009] In another variant of the life improving process, a chromiumnitride coating is provided which is capable of providing an equivalentor better life at a 50-60% cost reduction. These coatings are providedon a base 17-4ph material with again a hardness in the range of H900 toH1150. The chrome nitriding is actually a PVD coating which has ahardness of 60-65RC with a thickness of approximately 3 to 5 mils. Suchchrome nitriding is also void of all surface cracks present intraditional chrome and because of this premature failure is nonexistentproviding very consistent and predictable life curves. The process canalso eliminate one finish grind operation and provide a uniformthickness.

[0010] It is contemplated that various changes and modifications may bemade to the surface treatment without departing from the spirit andscope of the invention as defined by the following claims.

What is claimed is:
 1. In a reciprocating piston pump for use withpaints and coatings, said pump having at least one of a piston rod andcylinder, the improvement comprising treating at least one of said rodand cylinder with an ion nitriding process.
 2. The reciprocating pistonpump of claim 1 wherein the base material for at least one of said rodand cylinder is a 17-4ph stainless steel.
 3. The reciprocating pistonpump of claim 1 wherein the base material for at least one of said rodand cylinder is treated via ion nitriding to a hardness of about RC-65to
 75. 4. The process of treating at least one of a reciprocating pistonpump rod and cylinder formed of a base material and comprising the stepsof: heat treating the base material to a hardness of about H-900 toH-1150; and ion nitriding said material to a hardness of about RC-65 to75.